1. Field of Invention
This invention relates to systems and methods of controlling chemical dosage and, more particularly, to systems and methods of controlling the addition of a treating agent that effects the reduction of odorous species in sewage transfer systems.
2. Discussion of Related Art
Sewage systems include conduits typically that collect and direct sewage and other waste streams, such as rain water, to a treatment facility. Such systems typically include various pumping facilities, such as lift stations, that facilitate the transfer of the water, including wastewater, to such treatment facilities. During transit, however, odorous species are typically generated. Such odorous species are objectionable when released or discharged. Untreated sewage generates multiple odor-causing compounds, but the most prevalent and most distinctive compound formed is hydrogen sulfide. Hydrogen sulfide has a distinctive odor that can be detected at concentrations as small at 0.1 parts per million (ppm). In addition to having an offensive odor, hydrogen sulfide can also be a health hazard. Concentrations of as low as about 100 ppm can numb the sense of smell while concentrations of about 500 ppm may lead to pulmonary edema and, significantly, concentrations above about 1,000 ppm can cause collapse and death in humans.
In addition to being a health hazard, hydrogen sulfide is also a corrosion hazard. The moist environment typical of sewer systems facilitates hydrogen sulfide oxidation to sulfuric acid, which in turn can attack the infrastructure components comprising concrete, composite and metallic pipes and other structures of the system. Systems that have been left untreated for prolonged periods are typically severely corroded and can prematurely fail. Accordingly, odor and corrosion control, and treatment systems and techniques are typically utilized to minimize or at least reduce the level of such species.
For example, Howe et al., in U.S. Pat. No. 3,300,304, disclosed the anaerobic treatment of organic industrial wastes in an artificial lagoon. List, in U.S. Pat. No. 4,446,031, disclosed a sewage treatment composition, its manufacture and use. Mouche et al., in U.S. Pat. No. 4,681,687, disclosed the use of alkali metal nitrates to inhibit H2S formation in flue gas desulfurization system sludge. Tatnall, in U.S. Pat. No. 5,500,368, disclosed finely divided anthraquinone formulations as inhibitors of sulfide production from sulfate-reducing bacteria. Further, Ballinger, Jr. et al., in U.S. Pat. No. 6,309,597, disclosed a method for reducing hydrogen sulfide level in water containing sulfate-reducing bacteria and hydrogen sulfide-metabolizing bacteria. Bowers, in U.S. Pat. No. 5,045,213, disclosed a wastewater treatment method and apparatus. Richards, in U.S. Pat. Nos. 5,200,092 and 5,336,431, disclosed a composition and method for sulfide control. Miklos, in U.S. Pat. No. 6,660,163, disclosed waste treatment with control over biological solids. Vineyard, in U.S. Pat. No. 6,576,144, disclosed a method and apparatus for pretreatment of wastewater streams by chemical oxidation.
Recently, it has been proposed via commonly owned U.S. Pat. Nos. Re 37,181 and Re 36,651 (the entire content of each is expressly incorporated hereinto by reference) that the addition of nitrate, typically via an aqueous nitrate salt solution, to sewage systems, waste treatment plants and other industrial waste applications containing dissolved sulfides typically results in the elimination or substantial reduction of the sulfides, as well as the elimination of other minor odors associated with other sulfur-containing compounds. It is also known that significantly raising the pH of water streams (i.e., to greater than 10) by addition of an alkaline material (i.e. sodium hydroxide, calcium hydroxide) causes significant reduction of biological activity that produces dissolved sulfide.